1. Field of the Invention
This invention relates to a snap fastener and a packaging bag having the snap fastener and, more particularly, is available in several fields such as the food industry, pharmaceutical preparations, and haberdashery.
2. Description of the Related Art
Several packaging bags which have, on an opening side thereof, a web-like snap fastener consisting of a male snap fastener half-member (herein after referred to as "male half-member") and a corresponding female snap fastener half-member (herein after referred to as "female half-member") capable of intermeshing each other so that the opening side of the packaging bag can be shut and opened repeatedly, have been used in the food industry, pharmaceutical preparations, and haberdashery. It is noted that there have been some proposed methods of producing such a packaging bag.
One of the known general methods to produce the packaging bag is to extrude a cylindrical film with the male half-member as well as the corresponding female half-member through an extruding die and the other is to preliminary produce a two-piece type snap fastener tape of which one is used as the male half-member and the other is used as the corresponding female half-member and to adhere/weld the tape on a base film as the packaging bag body by means of a thermal adhesion method or an adhesive agent.
The former method involves some problems such that there is a limit in variety of applicable resins, it is inapplicable to laminated films, it can not be adapted to needed sizes of the packaging bag, and it can not be printed on easily, so that this method is restricted to produce general-purpose packaging bag. As the latter method has some advantages in applications to various size bags, dealings and costs because the packaging bag can be produced by a combination with the tape with snap fastener and the base film, this method is more popular than the former method.
The materials for the snap fastener are preferably low-density polyethylene (LDPE), polypropylene (PP) or the like so that the snap fastener can be adhered to the base film made from the same resin. Therefore, if an outer layer of the base film where the snap fastener is attached is made from LDPE, the snap fastener should be produced from LDPE, too.
However, the snap fastener made from LDPE or PP tends to not obtain enough adhesion to the bag body at a low heating temperature. When the packaging bag with the snap fastener made from LDPE is sterilized by boiling, some problems to be avoided will take place.
Accordingly, it is an object of the present invention to provide a preferable snap fastener and packaging bag with the same, in which a reliable adhesion at a low temperature and a greater heat-resistance can be obtained.